1. Field of the Invention
The present invention relates to an ignition coil for internal combustion engine that supplies a high voltage to a spark plug of an internal combustion engine.
2. Background Art
A core of a closed magnetic circuit configuration used in an ignition coil for internal combustion engine in the related art is formed of a center core disposed on an inner side of a primary coil and a secondary coil and a side core whose one end face abuts on one end face of the center core and the other end face abuts on the other end face of the center core via a magnet. Even when dimensions of the center core, the magnet, and the side core vary to some extent, deterioration in workability when assembling respective components is prevented by dividing the side core into two parts (see, for example, Patent Document 1).
Patent Document 1: JP-A-2006-294914
According to the ignition coil for internal combustion engine in the related art, because the side core is divided into two parts as described above, displacement at divided surfaces gives rise to magnetic circuit resistance, which deteriorates performance of the ignition coil. In order to lessen the displacement at the divided surfaces, the divided surfaces are formed diagonally. When viewed microscopically, however, it has been impossible to avoid a generating factor of the magnetic circuit resistance due to production tolerance, such as sagging occurring when the core is punched out with a mold. In order to reduce the magnetic circuit resistance, it is necessary to laminate a large number of magnetic steel sheets by adopting the thinnest plate possible as a core material, and further to perform processing, such as edge working on a punched sagging surface in a downstream process.